In a lot of ways, Prince’s Sign “O” The Times, which celebrates its 25th anniversary tomorrow, is the last great double-album of the LP era. When I bought a used-CD version years after it came out, I remember being a bit weirded out: The 79-minute album could just barely fit on one 80-minute CD, but the still came packaged in two separate CD cases, both of which looked almost exactly the same and which were held together with a rubber band when I bought them. If Prince or his label wanted to make things easy on the customers, they could’ve just thrown it all onto one disc. But user-friendliness wasn’t the point. The point was that Prince was joining a long and distinguished listeners here, throwing all his sprawling ambition out there on one piece of work and daring the universe to catch up with him. Sign “O” The Times is pretty staggering in its breadth, with its 16 songs veering wildly from one genre to the next and taking on big subjects with slippery panache. It’s the moment where Prince, who’d long known that he was a genius, made absolutely certain that the rest of the world knew it as well.

As with all great artists, we can divide Prince’s career up into interlocking chronological periods. And when Prince released Sign “O” The Times in 1987, he was a few years removed from one period ending. As an era-defining pop superstar, Prince had peaked with Purple Rain — both the classic album and the still-kinda-underrated movie — in 1984. Since then, he’d folded inward to an extent. Under The Cherry Moon, his next movie, was a notorious bomb. Around The World In A Day and Parade, his next two albums, were two of his least satisfying and successful, though the latter did give us “Kiss.” But that downward career turn almost happened by design. Purple Rain had been a Moment, and unlike other superstars of the era, Prince knew that he couldn’t just come back and make something bigger than that. So he went a different route instead, turning towards a flowery, vaguely Beatles-informed smooth-rock psychedelia, a sound that didn’t come as naturally to him as the muscular new-wave funk-pop that had made him famous. Sign “O” The Times, which Prince had wanted to make a triple-album at first, didn’t serve as a return to Purple Rain-era sales dominance, but it did something arguably even more valuable. It crystallized all the artistic experimentation of those previous two albums into something huge and tangible, displaying Prince as a musical adventurer without equal. Prince tries out a ton of different musical ideas on the album, and he nails almost all of them. It’s a thing to behold.

The album-opening title track is the one that announces the album as a grand statement, an everything-is-wrong harangue along the lines of “What’s Going On.” Its actual content is a little goofy; I don’t know how worried Prince really was about the teenagers whose “idea of fun is being in a gang called the Disciples, high on crack, toting a machine gun.” (This has always bugged me: Why did he specify the gang’s name? And was he talking about the Chicago-based Gangsta Disciples in particular?) But the bubbling, minimal, uncanny backing track, like a lot of other stuff on the album, predicts the warped and dubbed-out R&B that Timbaland would get famous making a decade later. “Slow Love” is a dizzy old-school R&B fuck-anthem that proves that Prince could’ve done just that for his entire career and made himself an immortal of the form. “U Got The Look” is pounding, glimmering new-wave with some surprisingly discordant guitar soloing. “If I Was Your Girlfriend” is cascading and virile top-40 stuff that would’ve fit just beautifully on Purple Rain. “Housequake” is what mid-’60s James Brown might’ve sounded like if he was really, really uptight, and the nine-minute “It’s Gonna Be A Beautiful Night” is an expansive funk throwdown where even the fake live-crowd noise is exactly in its place.

For a lot of people, the album’s real classic is “Adore,” the album’s closer and the one that pushes Prince’s soul showman side toward its platonic ideal, ducking and feinting away from obvious crowd-pleasing moments but still hitting titanic falsetto high notes at every available opportunity. But my two favorite songs on the album are the ones that step the furthest away from what Prince is supposed to be good at. The utterly gorgeous “Starfish And Coffee” is practically a Suzanne Vega song; it’s jazzy singer-songwriter pop with gospel-style backing vocals, fluttery harp runs, gigantic drums, and lyrics that, on the chorus, lovingly detail someone’s psychedelic breakfast. It makes no sense whatsoever, and it’s one of the single prettiest things Prince ever recorded. “The Cross,” meanwhile, is straight-up epic-rock power-balladry, like Prince looked hard at what U2 were doing in the same moment and then decided to top it. Those two songs make up a pretty stunning argument: Prince wasn’t just great when he was stepping out of his comfort zone. He was best when he was doing it.

Even with all its big leaps and breathtaking landings, I can’t say that Sign “O” The Times is Prince’s best album. I’d give that distinction to Purple Rain. On that one, Prince didn’t divide up all his gifts into different songs; he found ways to incorporate all of them into every song without making them sound like hypercrammed messes. But Sign “O” The Times is probably Prince’s most complete piece of self-presentation, the best possible example of how he wanted the world to see him. It’s an absolute essential, one of a handful in the man’s catalog.

Obviously, there’s a lot to talk about with this album. What’s your favorite song from it? Your favorite moment? Where do you think it fits in the overall arc of Prince’s career? Leave your thoughts in the comments section below.